There’s nothing worse than waking up in the middle of a super restful sleep cycle, whether you are startled by the neighbor’s dog or an unwanted text message. That feeling has a name. Sleep inertia happens when you wake up from deep sleep, and it can cause slow reaction time, irritability, grogginess and confusion. 

According to recent research from the Centers for Disease Control and Prevention, around 54% of adults wake up feeling well-rested. But when it comes to getting the most restful sleep overall, and getting back to sleep in a timely manner, not all wake-ups are equal.

What happens when you wake from a deep sleep

In one small study, participants were told to sleep during automated drives, then researchers analyzed how well they did taking back over the driving task to determine their number of driving errors and other analyses. Sleepiness was higher after a “light and stable” sleep, and there was a significant increase in driving errors after waking from “deep and stable sleep.”

“The sleep cycle is the rhythm a person’s body goes through when it is falling asleep/sleeping.  It consists of two states: non-Rapid Eye Movement Sleep (NREM) and REM. NREM is further broken down to N1, N2 and N3, which are sleep onset, light sleep and slow wave or deep sleep, respectively,” says Dr. Kavosh Rouhani, board-certified internist and board-eligible psychiatrist at Psychiatry Connection.

The research above showed that distribution of sleep stages and the stage prior to waking, not duration, can impact the possibility of sleep inertia.

Rouhani adds that our typical sleep cycle changes with illness and age, but typically lasts 90 to 120 minutes and repeats four to six times per night.

“N3 or slow wave sleep (is hardest to wake from) because it is the deepest stage of sleep. This is where your body recovers and it is required to feel rested on awakening,” he adds. “In early awakening, those in deep sleep are forced to recover from a much lower level of brain activity, which leads to prolonged sleep inertia, a transient state of impaired cognition and alertness on awakening.”

How to prevent sleepiness from ‘waking up at the wrong time’

Rouhani shares that it’s a common misconception that there is a universally right or wrong time to wake up. Instead, those trying to optimize sleep should have consistent sleep and wake times every day, even on weekends. Also, he recommends a wake-up time that allows for morning light exposure, to help maintain a synchronous circadian rhythm. That means no fast wake-ups followed by checking your phone right away.

Also, he hopes people don’t chalk up poor sleep to waking up at the wrong time, and instead fully assess sleep issues with a physician. “While poor sleep habits are often the cause of morning grogginess, there are also many illnesses that can contribute to poor sleep quality that unfortunately cannot be overcome with technique,” he says. “Speaking to your primary care doctor or a sleep medicine specialist can elucidate the cause and identify techniques or treatments that may be particularly helpful in your situation.”